Cylindrical developer carrier and production method thereof

ABSTRACT

A cylindrical developer carrier capable of fully charging a toner compound on a developing sleeve via frictional force even after being used repeatedly. The cylindrical developer carrier includes an electrically conductive substrate having an evenly roughened surface, and an alumite layer formed on the roughened surface, wherein the alumite layer has a uniform distribution of minute holes that reach the substrate surface. A method for manufacturing the cylindrical developer carrier includes roughening the electrically conductive substrate surface by blasting it with spherical fine particles, forming the alumite layer on the roughened surface by an anodizing method, and blasting the surface of the alumite-layer with amorphous fine particles that a diameter greater than that of the spherical fine particles.

FIELD OF THE INVENTION

The invention relates to a cylindrical developer carrier loaded on anelectrophotographic apparatus such as an electrophotographic printer,copying machine, or fax machine.

DESCRIPTION OF BACKGROUND ARTS

Conventionally, any electrophotographic apparatus, such as a laserprinter, LED printer, or copying machine using normal paper, executesthe formation of images through application of a so-called Carlsonprocess. The Carlson process is a method for forming an image via theoutput of a toner image transcribed and fixed on copy paper or the likeevery cycle of an electrophotographic process executed via componentsfor performing an electrification (i.e., charging), an exposure, a tonerdevelopment, an image transcription, and an electrical discharge. Suchcomponents respectively are disposed on the circumferential surface of acylindrical photoconductor provided with a photosensitive layer.

In the course of executing the above processes, when a static latentimage formed on the surface of the photoconductor via the aboveelectrifying and exposing steps is converted into a positive image inthe following toner developing step, toner compound stored in adeveloper unit is held and carried to an area close to the surface ofthe photoconductor through the application of a static electrical forcevia a cylindrical developer carrier, i.e., via a developing sleeve,before the static latent image present on the surface of thephotoconductor is eventually developed into a positive image. In orderto secure a satisfactory image via the above developing method, it isextremely important that the toner compound on the developing sleeve beheld and carried as a leveled layer free from the generation ofdeflection.

Likewise, when an excessively thick or thin toner layer is formed on thedeveloping sleeve, in terms of developing density, a satisfactory imagecannot be obtained. To prevent this, aside from the need to separatelyprovide the system with a specific member for regulating toner thicknesson the developing sleeve, in uniformly distributing toner compound overthe entire developing sleeve, surface conditions of the developingsleeve are also quite important. A fully smoothed surface is not alwaysthe optimal choice. It is, rather, conventionally considered to be moreadvantageous to provide the surface of the developing sleeve withprojections and recesses each having appropriate magnitude so as toenable optimum friction force to be generated between the developingsleeve and the toner compound. On the other hand, depending on thehardness of the developing sleeve, these projections and recesses aresubject to wear after repeated use. This causes the quality of images tobe gradually degraded, thus leading to a problem. To cope with thisproblem, an improvement in wear-resistance properties has been sought bythose concerned. In cases in which a developing sleeve is made of analuminum alloy, its Vickers hardness is rated to be as low asapproximately 70 Hv. Thus, it is known that wear-resistance propertiescan be improved through the formation of an alumite surface layergenerated by anodization with a Vickers hardness as high asapproximately 200 to 400 Hv after completing formation of projectionsand recesses on its surface (refer to the Laid-Open Japanese PatentPublication No. HEISEI 5-46008/1993).

On the other hand, in cases in which an alumite layer has been formed onthe surface of the developing sleeve, due to the insulationcharacteristics of the alumite layer, its surface resistance rises.However, in the case of a high surface resistance value, the chargeborne by the toner compound in the area corresponding to the spot forforming an image applied during the preceding developing process is aptto remain as it is without fully shifting onto the surface of thephotoconductor from the developing sleeve. As a result, the amount ofcharge in a specific area of the developing sleeve corresponding to theabove-described spot becomes greater than the amount of charge in thoseareas without the formation of images. As a result, when another imageis formed in the ensuing developing step, in the above specific area ofthe developing sleeve corresponding to the spot at which the last imagewas formed, developing-agent is further drawn toward another specificarea of the developing sleeve containing a higher charge. Thereby, thetoner compound becomes more difficult to shift onto the surface of thephotoconductor. This in turn leads to another problem in that adifference in depth is apt to be generated on the developed image of thephotoconductor through the generation of a specific patterncorresponding to the image generated during the last developing process.In other words, a so-called “ghost image” is apt to be generated. Insummary, the above symptom of a defect may be defined as the differencein the developing capability in correspondence with the tonerdevelopment history (hereinafter also referred to as “memory”).

In consideration of the technical problems described thus far, theinvention aims at providing a novel cylindrical developer carrier and amethod for manufacturing it, wherein the cylindrical developer carrieris capable of fully charging a toner compound on a developing sleeve viafriction force even after being used repeatedly. The invention also aimsto provide a cylindrical developer carrier wherein toner compound in theform of a leveled (even) layer can be properly held and carried, and thecylindrical developer carrier does not generate even the slightestdifference in developing capability in correspondence with the tonerdevelopment history.

SUMMARY OF THE INVENTION

According to the invention, the above-specified object has been achievedthrough the provision of a novel cylindrical developer carrierincorporating an alumite layer coated on a uniformly roughened surfaceof an electrically conductive substrate. The alumite layer uniformlyincorporates minute holes reaching the above-described conductivesubstrate.

According to another aspect of the invention, the cylindrical developercarrier is provided with an electrically conductive substrate consistingprimarily of an aluminum-group metallic material. According to a furtheraspect of the invention, the cylindrical developer carrier is composedof an alumite layer formed through the application of an anodizingmethod. According to still another aspect of the invention, thecylindrical developer carrier is composed of an alumite layer havingminute holes sealed with nickel acetate. The alumite layer may have athickness of 2 μm to 5 μm. According to a further aspect of theinvention, the minute holes account for 10% to 50% of the total area ofthe formed alumite layer that constitutes the cylindrical developercarrier.

According to an embodiment of the invention, a first method formanufacturing the inventive cylindrical developer carrier includes thefollowing steps: Initially, the surface of an electrically conductivesubstrate is roughened uniformly by blasting spherical fine particlesonto the surface. An alumite layer is formed using anodization. Thesurface is blasted with amorphous fine particles, each having a diametergreater than that of said spherical fine particles.

According to another embodiment of the invention, a second method formanufacturing the cylindrical developer carrier includes the followingsteps: Initially, spherical fine particles, including glass beads, areblasted onto the surface of an electrically conductive substrate. Analumite layer is formed by anodization. Then the surface is blasted withamorphous fine particles consisting primarily of aluminum oxide, witheach particle having a diameter greater than that of the spherical fineparticles.

According to a further embodiment of the invention, a third method formanufacturing the cylindrical developer carrier includes the followingsteps: Initially, spherical fine particles, including glass beads, areblasted onto the surface of an electrically conductive substrate.Projections and recesses are formed each being provided with a meansurface roughness in a specific range expressed in terms of Ra=0.8 μm to1.5 μm. An alumite layer is formed by anodization. Lastly, the surfaceis blasted with amorphous fine particles consisting primarily ofaluminum oxide, and each particle has a diameter greater than that ofsaid spherical fine particles.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view of the cylindrical developer carrieraccording to an embodiment of the invention;

FIG. 2 is a partially enlarged cross-sectional view of a cylindricaldeveloper carrier according to an embodiment of the invention; and

FIG. 3 is a schematic cross-sectional view of an image forming apparatusloaded with a cylindrical developer carrier according to an embodimentof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying drawings, preferred embodiments ofthe cylindrical developer carrier according to the invention aredescribed below. However, it should be understood that the scope of theinvention is by no means limited to the embodiments described below.

FIG. 1 is a perspective view of a cylindrical developer carrier, i.e., adeveloping sleeve 11, according to an embodiment of the invention. FIG.2 is a partially enlarged cross-sectional view of the developing sleeve11. FIG. 3 is a schematic cross-sectional view of an image formingapparatus 100 loaded with the developing sleeve 11 according to anembodiment of the invention.

Referring to FIG. 3, the image forming apparatus 100 includes a varietyof electrophotographic processing members, including a toner developingunit (consisting of a roller electrifying (charging) member 3, an imageexposing means 4, including an image exposing light source, adeveloping-agent storage tank 5, and a developing sleeve 1, an imagetranscribing unit 6, and a discharging member 7. These membersrespectively are disposed on the external circumferential surface of acylindrical electrophotographic organic photoconductor 10.

The image forming apparatus 100, which is based on the contact (roller)charging system shown in FIG. 3, serially executes electrophotographicprocesses through application of the above-described developing members,before eventually forming a predetermined image. A method of forming animage is described below. Initially, a predetermined voltage is added tothe roller charging member 3 disposed in contact with the surface of thephotoconductor 10. This electrifies the entire surface of thephotoconductor 10. Next, through the application of the image exposingmeans 4, an image corresponding to a predetermined document is exposedto the surface of the photoconductor 10, thus forming a static latentimage. Next, a toner compound, previously stirred and electrified in thedeveloping-agent storage tank 5, is statically transferred and adheredto the circumferential surface of the photoconductor 10 via thedeveloping sleeve 11, before the static latent image on thephotoconductor 10 is converted to a visible positive image. Next, thetoner image formed on the surface of the photoconductor 10 istransferred or transcribed onto an image material such as paper fed viaa paper-feeding roller and a paper-feeding guide member. The transfer isperformed through the application of the transcribing unit 6. Finally,residual toner compound remaining on the photoconductor 10 withouthaving been transcribed onto the sheet is collected by a cleaning member12. In the event that a residual charge still remains inside thephotoconductor 10, it is suggested that the residual charge beeliminated through the application of an adequate voltage or light beamsto the photoconductor 10 via the discharging means 7. On the other hand,the sheet material onto which a transcribed toner image is formed istransferred to a fixing unit (not shown) via a conveying unit, thusenabling the toner image to be fixed before eventually being output as avisible positive image.

In the image forming apparatus 100, the light source for the imageexposing means 4 may consist of a halogen lamp, a fluorescent lamp,laser beams, or the like. It is also permissible to add any auxiliaryprocessing step, as required. In addition to copying machines, the imageforming apparatus 100 may also be applied to a wide variety ofapplicable electrophotographic devices, such as a laser printer or anelectronic photoengraving system, for example.

As shown in the perspective view illustrated in FIG. 1, the developingsleeve 11 consists of a 20 mm-diameter sleeve-shaped electricallyconductive substrate 1 fitted with a pair of shaft holders on bothsides, which is made entirely of aluminum alloy. The actual diameter maybe adjusted according to the type of component loaded. Normally, thediameter will be in a range from 10 mm to 25 mm. In the above-citedexample, the aluminum alloy is made entirely of the compositioncorresponding to the JIS-A6063 standard. However, an aluminum alloyconforming to the JIS-A5056 or JIS-A3003 standard may also be used. Thealuminum sleeve substrate 1 is formed in accordance with thebelow-described series of steps. Initially, the original pipe ismanufactured by processing an aluminum-alloy ingot using an extrudingmachine and a drawing machine. Next, the surface of the formed originalpipe is planed or ground using a cutting tool or a grindstone until thepipe surface is completely smoothed. Next, through the application of anumber of spherical glass beads, having a maximum mean particle size of44 μm (#600), the surface of the sleeve substrate 1 is treated using ablasting process until recesses and projections created thereby producea mean surface roughness value Ra in a predetermined range, from 0.8 μmto 1.5 μm. It should be noted that, if the mean surface roughness valueexceeds 1.5 μm, toner compound will remain in the recessed portions.Conversely, if the mean surface roughness value is less than 0.8 μm, theeffect of the frictional charge that can be borne by the toner compoundwill become insufficient, resulting in a poor density of the tonercompound. This latter circumstance may lead to a failure to achieveproper density in images. Further, inadequate mean surface roughnessleads to slippage of the toner compound. Therefore as a result of whichthe toner layer will not be uniform due to uneven propagation of thetoner.

Next, through the application of an anode-oxidizing process against theroughened surface of the sleeve substrate 1, an alumite layer 2 isformed and then sealed. The sealing process preferably is executedthrough the application of nickel acetate. However, the invention alsois realizable with the use of sealing methods. It is preferred that thealumite layer 2 be provided with a thickness in the range from 2 μm to amaximum of 5 μm. If the thickness exceeds 5 μm, it will become quitedifficult uniformly to form a plurality of minute holes 21 reaching thealuminum substrate 1 according to the invention, as described below.Conversely, if the above thickness is less than 2 μm, the alumite layer2 will wear quickly.

After the above alumite layer 2 has been formed, a plurality of minuteholes 21 are formed by blasting the layer surface with fine particles ofamorphous aluminum oxide (alumina), each having a hardness value greaterthan that of alumite. Insofar as the hardness value is greater than thatof alumite, it is also possible to use fine particles of anothermaterial. The particle size (such as #320) of the usable alumina fineparticles shall be greater than the particle size (such as #600) of theabove-described glass beads.

The object of the blasting process following the formation of thealumite layer 2, and the details of the process are described below.Initially, among the projections and recesses formed on the alumitelayer 2, only the alumite layer 2 immediately above the projections isremoved. Then, a plurality of uniformly distributed minute holes 21reaching the aluminum substrate 1 are provided so as to provide aplurality of uniformly distributed leakage sites for allowing leakagefrom the charge borne by the toner compound. Thereby, the surfaceresistance value of the alumite layer 2 is minimized, which solves theabove-described technical problem arising from a difference in thedeveloping capability in correspondence with the surface's tonerdevelopment history.

EXAMPLE

In order to accurately determine the relationship of quality of imagesto the ratio of the area of the minute holes formed immediately abovethe projections on the alumite layer 2 to the area shared by the formedalumite layer 2, the inventors conducted experiments. Initially, actualsamples of the developing sleeve 11 were prepared, and were individuallyprovided with ratios 5%, 10%, 20%, 40%, 50%, 60%, 70%, and 100% of thetotal area of the minute holes 21 to the actual area shared by thealumite layer 2 (hereinafter total ratios). The total area ratios werecomputed based on the difference in the light reflection ratios asbetween the alumite-layer formed portions and the minute holes 21. Moreparticularly, a light-reflection rating instrument was used, with whichthe total area ratios of the minute holes 21 were computed based on acalibration curve prepared from a previously known sample.Alternatively, it is also allowable to compute area ratios by referringto an enlarged photographic view of the sleeve surface. The computedresults are shown in TABLE 1.

Then, the actual quality of the formed images and actual service life ofthe developing sleeves 11 were respectively evaluated. Through theapplication of a Macbeth densiometer, the density of images wasevaluated, with ratings of 1.3 and above 1.3 designated by circularsymbols (o), ratings of 1.2 to 1.3 designated by triangular symbols (Δ),and ratings below 1.2 designated by a cross symbol (x), as shown inTABLE 1 below. It is understood from the results of evaluation of thedensity of images that the toner compound was fully subjected tofriction, and the subsequent charge was applied to the developing sleeve11 before being formed into a level layer of toner compound, which wasthen properly held and carried without generating any deflection.

Following evaluation of an image memory (toner development history) tocheck for a difference in the toner developing capability, the resultsshowing non-occurrence of a difference in the developing capability weredesignated by circular symbols (o) in TABLE 1 below. The results showingthe occurrence of some difference in the toner developing capabilitywere designated by a triangular symbol (Δ). The results showing theactual occurrence of a difference in the toner developing capabilitywere designated by cross symbols (x). It is thus understood from theresults of evaluation of the image memory shown in TABLE 1 that thedeveloping sleeve 11 retained a proper surface condition through thepreservation of appropriate leakage sites, without generating anydifference in the toner developing capability in correspondence with thetoner development history.

To evaluate the actual service life of the developing sleeves 11, up tomore than 20,000 copies were prepared with each sleeve. Those sleevesfound to be sufficiently durable after the processing of more than20,000 copies were designated by circular symbols (o). Those sleevesfound to be sufficiently durable for processing only 10,000 to 20,000copies were designated by triangular symbols (Δ), whereas those sleevesfound to be insufficiently durable to process even 10,000 copies weredesignated by cross symbols (x) in TABLE 1 below. Thus, the results ofevaluation of the actual service life of the developing sleevescorresponding to the former two groups enabled the inventors to detectthe presence or absence of variations in (or degradation of) thephysical characteristics of the developing sleeves as between an initialstate and after use to prepare a predetermined number of copies.

To define the overall results of the evaluations of the groups ofsleeves with the respective minute hole area ratios, results evaluatedas (o) in all three categories were rated with a designation (o). In theevent that even a single characteristic was rated with a cross symbol(x), the overall evaluation result for the group of sleeves wasdesignated by the cross symbol (x) as well. Those sleeve groups forwhich at least one characteristic was designated by the triangularsymbol (Δ), without the presence of a designation with the cross symbol(x), were identified with the triangular symbol (Δ) in the designationof their overall evaluation result. TABLE 1 Minute hole Image ImageSleeve Overall area ratio (%) density memory life evaluation 5 ∘ x ∘ x10 ∘ ∘ ∘ ∘ 20 ∘ ∘ ∘ ∘ 40 ∘ ∘ ∘ ∘ 50 ∘ ∘ ∘ ∘ 60 ∘ ∘ Δ Δ 70 Δ ∘ x x 100 x∘ x x

With reference to TABLE 1, the above three characteristics (imagedensity, image memory, and sleeve life) were evaluated as (o) when thearea ratio of minute holes to the area shared by the alumite layerformed on the surface of the developing sleeve ranged from 10% to 50%,and it is thus clear that the overall evaluation result for thesedeveloping sleeves was favorably designated to be (o) as well.

Thus, according to the invention, an alumite layer is provided bycoating over the entire surface of an electrically conductive substratethat has been uniformly roughened, wherein the alumite layer itselfconstitutes a cylindrical developer carrier evenly incorporating minuteholes respectively reaching the surface of the above-describedsubstrate. Due to this construction, even after repeated use, tonercompound can be subjected to and hold a full, evenly propagatedfrictional charge on the developing sleeve, thereby enabling theinvention to provide a novel cylindrical developer carrier withoutgenerating any difference in the toner developing capability incorrespondence with the toner development history.

1-12. (canceled)
 13. A cylindrical developer carrier comprising anelectrically conductive substrate having an evenly roughened surface;and an alumite layer formed on said surface, wherein said alumite layerhas a uniform distribution of minute holes respectively reaching saidsubstrate surface.
 14. A cylindrical developer carrier according toclaim 13, wherein said electrically conductive substrate is formedprimarily of an aluminum-group metallic material.
 15. A cylindricaldeveloper carrier according to claim 13, wherein said alumite layercomprises an alumite layer formed by an anodizing method.
 16. Acylindrical developer carrier according to claim 15, further comprisingnickel acetate sealing said alumite layer.
 17. A cylindrical developercarrier according to claim 13, further comprising nickel acetate sealingsaid alumite layer.
 18. A cylindrical developer carrier according toclaim 17, wherein said alumite layer has a thickness in the range of 2μm to 5 μm.
 19. A cylindrical developer carrier according to claim 13,wherein said alumite layer has a thickness in the range of 2 μm to 5 μm.20. A cylindrical developer carrier according to claim 19, wherein saidminute holes, as a whole, account for 10% to 50% of the total area ofthe alumite layer.
 21. A cylindrical developer carrier according toclaim 13, wherein said minute holes, as a whole, account for 10% to 50%of the total area of the alumite layer.
 22. A method for manufacturing acylindrical developer carrier comprising the steps of: roughening anelectrically conductive substrate surface by blasting spherical fineparticles onto the substrate surface; forming an alumite layer on theroughened surface by an anodizing method; and blasting the surface ofthe alumite-layer with amorphous fine particles each having a diametergreater than that of the spherical fine particles.
 23. A method formanufacturing a cylindrical developer carrier according to claim 22,wherein the blasting the spherical fine particles includes blasting theelectrically conductive substrate surface with glass beads, and theblasting the surface of the alumite layer with amorphous fine particlesincludes blasting the alumite layer surface with amorphous fineparticles formed primarily of aluminum oxide, each of the amorphous fineparticles having a diameter greater than that of the spherical fineparticles.
 24. A method for manufacturing a cylindrical developercarrier according to claim 23, wherein the step of blasting saidelectrically conductive substrate surface with spherical fine particlesincludes a step of blasting the substrate surface with spherical fineparticles consisting solely of glass beads, so as to form a number ofprojections and recesses each having a mean surface roughness rated atRa=0.8 μm to 1.5 μm, and the blasting the surface of the alumite layerwith amorphous fine particles includes blasting the alumite layersurface with amorphous fine particles formed primarily of aluminumoxide, each of the amorphous fine particles having a diameter greaterthan that of the spherical fine particles.